This invention relates to cathodic protection anode assemblies which are suitable for cathodic protection of marine, and other submergeable, structures. The invention also provides a new reference electrode, methods of cathodically protecting structures and structures so protected.
Cathodic protection is the chief line of defence for corrosion control of steel structures in a marine environment. Whilst sacrificial anodes may be used for this purpose, the design lives of 25 to 30 years which have been specified as the theoretical maxima for such anodes are open to doubt. Sacrificial anodes do, of course, have the advantage that they provide immediate protection of the structure when submerged. Impressed current systems for cathodic protection require a DC power supply, and there may be considerable delay due to other constraints in providing this effectively in an offshore structure. Furthermore, existing impressed current systems are based on long life anodes with heavy coatings of platinum on, for example, a substrate of niobium. Such anodes are extremely expensive.
It will be apparent that in many circumstances, the provision of a relatively short to medium life system would have considerable advantages (say from 3 to 10 years in expected lifetime). Such an impressed current anode system should be relatively cheap and easy to install. All impressed current anodes have the great advantage that their output and effectiveness can be monitored and they are extremely easy to control.